Carburetor system

ABSTRACT

Method and means for precisely and continuously controlling the strength of the fuel-air mixture in an injection carburetion system for Otto engines is disclosed, wherein the fuel flow rate is continuously adjusted as a function of a signal as obtained from a pneumo-hydraulic unit, wherein the fuel flow rate as a pressure differential is compared with the air flow rate, as a pressure differential also, the said pneumo-hydraulic unit comprising a moving element, responsive to the difference of the above said air and fuel pressure differential, and controlling the fuel feed into the carburation system whereby the mixture strength is kept essentially constant.

omdmm m 0 m n g 32 mmneu P, k wm cw s amm m m. e onvn E a b y m mw .m .m am n a w n tw nr. e nD n d a e. O t7 fifl e a m m dP Lmom mn S .m e ei.y r rt yl u c e n U C an e n a B flbr t 1 fn w tn Pu ea m m h u m mm U 1 ,m wmw e e m rwmm rhspt.m 2 AAA flA 999 9 6MNM66N 2 1 1221 .666 .6 222 2 Lucio Bergamini, Via Todeschini, 8, 37100 Verona, Italy Filed: Mar. 16, 1972 Appl. No.: 235,191

u.s. c|....... 261/39 A, 123/139 AW,

261/52, 261/69 A Int. F02m 69/04 Field of Search... 261/69 A, 39 A, 39 R, 39 B, 261/39 D, 52, 50 R, 51; 123/139 AW References Cited UNITED STATES PATENTS United States Patent Bergamini CARBURETOR SYSTEM [76] Inventor:

Richardson.......

m mrnm n ha n n nuu "m uuDm U u n yun n n mwflmmeo 1 t e ora I .lr 1 E SBM MBS 7970 369 23455555 99999999 l/HHHHHH 47950322 1 07 492 64496403 35692333 26207337 1 2222222 PATENTEDAPR 30 I974 3301.710 SHEEI 2 (W4 CARBURETOR SYSTEM The present invention relates to a method and means for continuously and precisely controlling the mixture strength in an injection carburetion system for engines operating according to the Otto cycle, at any speed of the engine and at varying temperature and pressure conditions of the air, as well as taking into account the possible clogging of the air filter.

It is well known that in the Otto engines, in order to compensate the non proportional intake rate with the air flow and therefore to obtain a constant fuel-air weight ratio, a series of adjustments is effected, whilst the final setting takes place by means of two adjusting screws only. Such a constant ratio, however, is not perfect at all the running conditions of the engine, the transient ones being also included, and furthermore the lower is the level of unburnt substances tolerable in the exhaust gas, the higher is the precision of the required tuning. Further, the carburetion of said standard carburettors with a stoichiometric mixture is rather difficult at low rpm of the engine due to the reduced turbulence which does not promote the fuel vaporization, so that the mixture must be enriched with the resulting exhaust of unburnt substances. Thus, in order to compensate the irregularities of the standard carburettors, i.e., to reduce the unburnt substances in the exhaust gases, the engines are generally provided with post-combustion systems, in which fresh air is blown and catalytic mufflers are used.

The problem of the precise control of the mixture at any rpm of the engine as well as the problem of the fuel atomization are on the contrary effectively solved in the injection carburetion systems. These injection systerns, well known from the prior art, either of the type provided with mechanical stabilizers of the mixture strength operating by stroke variations of pistons, or of electronic type in which the open condition time of electrovalves is modulated, in comparison with the afore said standard carburettors are structurally and operatively cumbersome so that they are much more costly and a more careful and skilled servicing is necessary.

In the prior art, are also known several proposals for carburetion systems based on fluidic components, fed by the fuel intake pressure; these proposals have not resulted in industrially acceptable devices due to the inaccuracy of the adjustment of the fuel flow rate which, being varied within a quite wide range, does not insure a reliable operation of said fluidic components.

The object of the present invention is that of overcoming the limits of the three above mentioned carburetion systems, whilst their essential advantages are maintained. in other words the present invention aims to provide a method and means for continuous and precise control of the mixture strength in an injection carburetion system of an Otto engine, at any engine speed and at any temperature and pressure conditions of the air, as well as for effecting a good atomization of the fuel at low rpm, as it occurs in the known injection carburetion systems, but avoiding their costly and cumbersomecharacteristics both of structure and of time up and servicing; these characteristics are instead comparable with those of the conventional carburettors (only two setting screws); lastly the same intake pressure of the fuel, as in the fluidic systems, is used as the energy source for the adjustment of the fuel flow rate, the adjustment taking place, however, according to pneumohydraulic units by which precision and reliability of the measured rate are ensured at every rpm value, such a result being not otherwise obtainable by a fluidic systern.

Another object of the present invention is to provide an easy and ready simultaneous setting both of the mixture strength and of the temperature and pressure compensation, such as to permit the method and means of the invention to be easily adapted to any type of engine without involving any detailed knowledge of the engine characteristics, except its maximum power.

The method of the invention is essentially characterized by a continuous adjustment of the fuel flow rate, unlike from a pulse control, as achieved by measuring said fiow rate as a signal of pressure differential across an orifice, partially closed by a shutter and by comparing said measured value of the fuel flow rate with the signal representing the measured air flow rate, as obtained in a similar manner, in a pneumo-hydraulic calculating unit, which, being only sensitive to the difference of the two afore said signals, control the fuel flow rate so that the mixture strength is kept constant.

More particularly, the method of the invention com prises measuring the fuel flow rate by determining the pressure drop, namely the presure existing upstream and downstream respectively of an orifice partially closed by a pin of a variable restriction device through which the fuel flows, as well as the air flow rate also by measuring the air pressure existing upstream and downstream respectively of a thin walled diaphragm, which is restricted by a shutter positioned within the carburettor casing, said pin and said shutter being connected by a lever mechanism both to each other and to the throttle of the carburettor so as to ensure an equal restriction of the diaphragm and of the orifice; transmitting the two air pressures thus measured upstream and downstream respectively of the said diaphragm so that they are compared in two opposed chambers, having equal effective areas, of a pneumo-hydraulic calculating unit, the moving element of which is therefore sensitive only to their difference; connecting the upstream portion of the orifice of the said variable restriction device to the outlet chamber of said calculating unit, the inlet chamber of which communicates with the said outlet chamber through a port choked by a shutter fixedly connected to the said moving element and is fed with the fuel sucked from the fuel tank by means of a pump and adjusted .to a constant static pressure by passing through a reducing filter; transmitting the fuel pressure existing downstream of the said orifice of the variable restriction device to a pressure regulating injector and to a reaction chamber of the said calculating unit respectively, the moving element of the latter being thus sensitive to the only difference between the fuel pressures respectively in the reaction chamber and in the outlet chamber, having equal effective areas; compensating then the variations of the air density by means of a thermo-barometric compensating device which varies the restriction of the orifice of the room temperature and of the pressure existing in the stagnation zone of the carburettor, i.e., downstream of the air filter, thus taking also into account the possible pressure drop resulting from the same filter being clogged.

According to a feature of the present method, both the said pin and the said shutter, by which the respective measurements of the fuel and of the air flow rates are effected by causing a pressure drop both in the fuel and in the air flow, are shaped so as to show equal percentage values, namely for a given small displacement either of the pin or of the shutter, the measured pressure drop being equal, a percentage variation of the respective flow rate occurs which is constant whatsoever is the pin or shutter position from which said displacement starts. .As a consequence a double advantage is achieved, namely both an easy setting of the mixture strength and a quite similarly easy compensation of the variations of the air density. In fact the adjustment of the ratio between the fuel flow rate and the air flow rate, i.e., the setting of the mixture strength can be now easily carried out by the mere axial displacement of the pin with respect to the orifice (thus varying the fuel flow rate), because the same pin, once it is upwardly or downwardly positioned, continues to ensure, on its movements as caused by the throttle, the proportioned variation of the two opening parts of the orifice and of the diaphragm and thus the ratio between the new fuel flow rate and the air flow rate is kept constant upon varying the engine rpm.

On the other hand in order to compensate the variations of the air density it is sufficient to connect the thermo-barometric element with the bottom part of the aforesaid variable restriction device, so that the thermal expansion of said thermo-barometric element due to the variations of the air temperature and pressure give place to a proportional displacement of said pin with respect to the orifice. According to one feature of the invention, the above said setting of the mixture strength and the thermal and barometric compensation are simultaneously achieved by means of only one adjusting screw, which against the opposing action of a spring, acts on the above said pin of the variable restriction device.

As a matter of fact, the above mentioned equal percentage characteristic is provided by suitably shaping the pin and the shutter according to an exponential law so as to cause a variation of the opening degree of the orifice and of the diaphragm corresponding to an exponential function with respect to the displacements of the pin and of the shutter.

According to a preferred embodiment of the invention the temperature and pressure variations of the air of the fuel-air mixture are measured by means of only one thermo-barometric capsule, tightly sealed and filled with air at the room pressure, which is enclosed within a casing, the latter being in turn connected through a duct to the air stagnation zone of the carburettor, so that said capsule is subjected to the pressure and temperature conditions of the air within the said stagnation zone. In fact a variation of the temperature shall cause an expansion of the air inside the capsule, whereas a variation of the pressure shall cause a like change of the capsule volume and thus a displacement will take place by which the position relationship between the pin and the orifice of the variable restriction device and therefore the fuel flow rate will be varied proportionally to the density changes of the air of the mixture. Of course any other type of compensation system for the air density may be used, e.g., bellows or a membrane element, in substitution for the capsule, or also two separate devices, like an aneroid capsule,

sealed under vacuum, for the pressure measurements, and a bimetallic plate for the temperature measuments, provided that these devices are capable of giving place to said displacements and thus proportionally varying the relative positions of the pin and of the orifice.

According to another feature of the method of the inventions the pressure of the fuel sucked from the fuel tank is adjusted by means of a reducing filter, before being fed to the pneumo-hydraulic calculating unit and a pressure adjusting injector is used, which comprises a variable position pin, by which, besides the fuel nebulization, the static pressure upstreams of the injector is caused to be constant on varying the fuel flow rate and on varying the pressure in the air intake duct of the carburettor.

As a consequence the measurement of the fuel flow rate takes place at constant static pressure with the obvious operation advantages as well as enhancing the structural simplicity of the pneumo-hydraulic calculating unit. In the latter unit, in fact, two fuel pressures and two air pressures are respectively compared in chambers having effective areas which are respectively equal and the moving element of said unit by means of the related shutter regulates the fuel flow port, thus adjusting the fuel flow rate as a function only of the difference of the difference between the afore said pressures and therefore independently from the static values of these pressures which, in the said comparison, are cancelled. Since then, the static pressure are constant, the effective areas of the chambers of the calculating unit need no longer to be equal, because any little difference causes a constant force to act on the moving element, which can be easily counterbalanced by a compensation spring.

According to a preferred embodiment of the invention, the pressure adjusting injector consists of a chamber, in which the fuel is fed, containing a moving element which, on one side, is provided with a conical pin partially closing the hole through which the fuel enters into the intake duct of the carburettor, thus being vaporized; on the other it is connected to a membrane of rubber or other materials, against which a setting spring acts, which is contained in another chamber communicating with the atmosphere, adiacent to the first one, the said membrane separating said two chambers.

Therefore the moving element takes an equilibrium position under the force of the fuel pressure acting on the effective area of the membrane and the constant spring force, the small position changes of the pin, in order to vary the flow rate of the fuel to be injected; thus occurring at constant static pressure.

Such a constance of the static pressure of the fuel in the injector, besides the afore mentioned advantage is further advantageous due to the more effective fuel atomization at the low rpm of the engine (slow running) because a high pressure drop between upstream and downstream of the fuel outlet hole is available, since the air pressure at such a running conditions in the intake duct of the carburettor is very low.

Moreover, in order to enhance the vaporization efficiency a vortex effect can be established either by providing both in the fuel chamber and in the pin corresponding helical grooves or by giving to the chamber the same conical shape of the pin and tangentially feeding the fuel into the said chamber.

Of course, to separate the two chambers of the injector, bellows or capsule means can be substituted for the membrane.

The pneumo-hydraulic calculating unit comprises, according to a preferred embodiment of the present invention a hollow body within which a moving element, by means of three elastic membranes of rubber or other material, forms the four chambers for the comparison of the two fuel pressures and of the two measured air pressures, the chambers being thus aligned on the same axis of the moving element, to the lower part of the latter a shutter being fixed which controls the communication port between the feeding chamber and the outlet chamber of the calculating unit, whereas to the opposite part of the moving part a compensation spring for the elastic pre-loads and for the force generated by the difference of fuel static pressure is provided.

According to another preferred embodiment of the invention, the four chambers for the comparison of the involved pressures, with the consequent adjustment of the fuel flow rate, of the pneumo-hydraulic unit are formed by means of membrane or bellows which, instead of being aligned on the same axis and acted on by opposed forces as in the preceding embodiment, are placed in line, each one near the next and acted on by forces all directed in the same direction, the equilibrium being obtained by means of a lever fulcrumed at the middle of its length by a pin, a flexible blade or a cross support formed by flexible blades acting as a balance, to which said bellows are fixed in pairs, symmetrically with respect to the fulcrum. Such a type of calculating unit is particularly suitable for use in the aviation engines since a better balancing in case of accelerations due to bounces, tilting or abrupt evolutions of the vehicle is permitted, inasmuch as no moving element is provided the weight of which would be involved causing the calculating unit to operate in overturned condition.

Lastly, as a peculiar feature of the method and means of the present invention, a correction of the mixture strength is effected in exceedingly easily way, such as a momentarily enrichment of the mixture for the cold starting of the engine, said correction being obtainable by acting either on the pneumo-hydraulic calculating unit, on the variable restriction device of the fuel flow rate or also on the kinematic linkage (lever mechanism) connecting the measuring member of the fuel flow rate to the measuring member of the air flow rate. In any case very simple mechanism are necessary and the intervention will be either of the manual type, by a mechanism directly controlled by the driver, or of the automatic type, wherein the mechanism is controlled by a simple electric thermostat, by a pneumatic thermodeviator or by a thermal switch mounted to the engine head. In the following some mechanisms and their operation will be described, in order to effect such a correction.

The invention will be better understood with reference to the enclosed drawings which show a preferred embodiment, having illustrative but not limiting purpose, sincev technical and structure modifications can be effected without falling out of the scope of the present invention. In the drawings:

FIG. 1 schematically shows some parts being in cross section, an injection carburetion system for Otto engines in which the adjustment of the mixture strength occurs by the method and means of the invention;

FIG. 2 is a front sectional view of a pneumohydraulic calculating unit of the fulcrumed lever type and wherein the chambers for the comparison of the involved pressures are formed by aligned bellows, according to one embodiment of the invention;

FIG. 3 is a front cross-sectional view of a pneumohydraulic calculating unit like that of FIG. 2, wherein the said chambers are formed by membranes, according to another embodiment of the invention; and

FIGS. 4 to 7 show several manners for the correction of the mixture strength, suitable for the cold starting of the engine.

With reference to FIG. 1, the reference number 1 indicates the carburettor body which is connected at the upper part to the air filter 2 and at the lower part to the intake duct 3. Within the carburettor body 1 there are mounted a pressure adjusting injector 4 and a throttle 5 which is controlled by the accelerator 6 for varying likewise the conventional carburettors, the air flow and therefore the mixture flow to the engine, in order to control the power delivered by the latter. The slow running screw 7 has the same function as in the conventional carburettors.

In the carburettor body 1, adjacent to the air filter 2, a thin walled diaphragm 8 is provided, the opening of which is choked by a shutter 9, whose shape follows an exponential law. The stem 10 of said shutter protrudes from the carburettor body 1, the seal being ensured by elastic gaskets 11, and is connected through a linkage pin 12, entering an opening 13, to one end of a lever mechanism 14, the other end of which is pivotally connected at 15 to a fixed part of the engine. Thus the oscillations of the lever mechanism 14 about the fulcrum 15 cause vertical displacements of the shutter 9 to take place.

A variable restriction device 16, connected to the same lever mechanism 14, is formed by a chamber, within which a thin walled diaphragm 17 defines an orifice 18 which is choked by a pin 19 also shaped according to the same exponential law as the shutter 9. A spring 20 pushes upwardly the pin 19, and is kept into the required position by a setting screw 21, which, being screwably mounted to the said lever mechanism 14 forms a shoulder for the said pin counteracting the action of the spring 20.

The lever mechanism 14 is in turn connected to the throttle 5 by a connecting rod, so as to ensure the same choking degree both of the diaphragm 8 and of the orifice 18 at each opening angle of the throttle.

The chamber of the variable restriction device 16 is vertically movable and at the lower part abuts the end of a coupling pin 23 passing through the wall of the casing 24 of the thermo-barometric compensation device, the seal being ensured by gaskets 25, and in turn has its other end engaging by abutment the thermobarometric capsule 26. Said capsule 26 is tightly sealed and filled with air at room pressure, whilst the casing 24 is rigidly mounted to the engine end is connected with the air stagnation zone 27 of the carburettor, immediately downstream of the air filter, through the duct 28. Thus, any variation of the air temperature or pressure will cause the volume of the thermobarometric capsule 16 to vary and therefore the relative positions of the pin 19 and the orifice 18, namely the fuel flow rate, will vary proportionally to the density changes of the air of the mixture.

ducts 35 and 36, is respectively connected with the reaction chamber 37 of the said calculating unit 32 as well as to the pressure adjusting injector 4.

Said injector 4 comprises a chamber 38, to which the fuel is fed, being separated from a chamber 39 communicating with the atmosphere by an elastic membrane 40. A moving element 41, which at one end inside the chamber 38 is rigid with the said membrane, terminates in a conical pin 42, choking the hole 43 through which the fuel is ejected as a spray into the intake duct 3, the pin 42 being counteracted by a setting spring 44 seated in the chamber 39. Thus the moving element 41 takes an equilibrium position under the force caused by the fuel pressure on the effective area of the membrane 40 and the constant force of the spring 44, and as a consequence the little position changes of the pin 42, to vary the flow rate of the fuel to be injected, take place at the constant static pressure due to the spring 44.

The said pneumo-hydraulic calculating unit 32 consists of a hollow body within which four chambers aligned with some axis of the moving element 45 are defined, by means of the three elastic membranes 46, 47 and 48, by the same moving element 45, namely an outlet chamber 31 for the fuel which, as already stated, is connected with the inlet 29 of the variable restriction device 16, a chamber of air pressure 49 which is connected through the duct 50 with the carburettor zone following the diaphragm 8 shutter 9 assembly, a second chamber of air pressure 51, which through the duct 51 is connected with the said air stagnation zone 27 in the carburettor and lastly the already mentioned reaction chamber 37 connected to the the outlet 33 of the variable restriction device 16. The moving element 45 in the lower part is provided with a shutter 53, by which the communication port between the outlet chamber 31 and the fuel feeding chamber 54 of the calculating unit is partially closed, whereas in the upper part is acted on by a spring 55 which, being adjustable by means of a screw 56 and acting on the moving element inside the reaction chamber 37, permits both the elastic pre-loads and the possible parasite forces, deriving from small differences between the effective areas of the air chambers and of the fuel chamber respectively of the pneumo-hydraulic calculating unit to be compensated in the setting phase.

The operation according to the method of the present invention is as follows.

The fuel, sucked from the tank 57 by means of the pump 58 which can be either of conventional mechanical engine driven type or of electric type, is filtered and has its pressure adjusted in the reducing filter 59 and passes then, through the duct 60, in the feeding chamber 54 of the pneumo-hydraulic calculating unit 32. In the said unit the shutter 53 operated by the moving element 45, controls the flow rate of the fuel which is fed to the variable restriction device 16, wherein the said flow rate of the fuel is measured by the orifice 18 partially closed by the pin 19 on the basis of the pressure drop occurring across the same orifice, whilst the connection between the outlet 33 of the variable restriction device 16 and the reaction chamber 37 of the calculating unit 32 causes said pressure drop to act on the moving element 45 of the said calculating unit as an upwardly directed force, which is proportional to the effective area of said membrane, independently from the value of the fuel static pressure. In fact the high pressure fuel is upstream the orifice 18 and operates the membrane 46 producing an upward thrust on the moving element proportional to the effective area of the membrane. The low pressure of the fuel is present, on the contrary, downstream the orifice 18 and, by acting on the membrane 48, originates a downwardly directed force.

The difierence between these two forces, namely the effective force acting on the moving element 45, is as a consequence upwardly directed and the equal extension of the effective areas of the above said membranes results in the cancellation, at the moving element, of the forces originated from the static pressure of the fuel, the effective force being thus only proportional to the pressure drop, namely to the flow rate of the fuel.

On the contrary, as already stated, possible parasitic forces due to the static pressure, in case the said effective areas of the membranes are not exactly equal, may be easily cancelled by means of the zero setting screw 56 by which the compensation spring is loaded, since the static pressure of the fuel is constant.

Furthermore, the connection between the pneumohydraulic calculating unit 32 and both with the stagnation zone 27 and the zone following the diaphragm 8 shutter 9 assembly, respectively through the ducts 52 and 50, transmits the measurement of the air flow rate, as indicated by the pressure drop across the said diaphragm 8 shutter 9 assembly, again to the moving element 45 of the said calculating unit, where a downwardly directed thrust is originated.

Summing up, the moving element 45 of the pneumohydraulic calculating unit takes an equilibrium position under the action of two thrusts, namely those due to the air and fuel pressures respectively, and then by means of the shutter 53 controls the thrust due to the fuel pressure, i.e., the fuel flow rate, so as to adjust it with respect to the air flow rate, the ratio between the flow rates of the air and of the fuel, namely the mixture strength, being always kept constant.

Thus, when the accelerator 6 and then the throttle 5 are actuated, a displacement of the shutter 9 and of the pin 19, through the connecting rod 22 and the lever mechanism, takes place with the consequent variation both of the air and of the fuel flow rates but, due to equal percentage characteristic of the shutter 9 and of the pin 19, it is ensured that said variations of the air flow rate and of the fuel flow rate are always proportional and therefore their ratio, i.e., the mixture strength, remains unchanged.

The adjustment of the said ratio between the air flow rate and the fuel flow rate namely the setting of the mixture strength, is then effected by'means of the setting screw 21 by which the position of the pin 19 of the variable restriction device 16 is adjusted, thus varying the opening of the orifice 18 and thereby the fuel flow rate. In addition, due to the connection type between the variable restriction device 16 and the thermo barometric capsule 26 of the pressure compensation device, not only the mixture strength but also the point of barometric and thermal compensation is adjusted by means of the said setting screw 21.

It is also to be taken into account that both the pneumo-hydraulic calculating unit 32, through the duct 52,

and the thermo-barometric compensation device, through the duct 28, are connected to the said stagnation zone 27, downstream of the air filter 2, to carry out, in this point, the measurement of the air density, in order to consider also the possible pressure drop due to te air filter being clogged.

As a conclusion, in the carburetion system according to the present invention only two adjustments must be effected, likewise the conventional carburettors. In fact, except the zero setting screw 56 which relates to the specific operation of the pneumo-hydraulic calculating unit 32 and may be once adjusted at the works by means of suitable testing equipment, only the adjustment of the slow running screw 7 and of the setting screw 21 is needed.

On flowing, the fuel is then fed from the variable restriction device 16 to the pressure adjusting injector 4 which, by giving to the fuel a rather high pressure level, which is constant on varying the fuel flow rate and the pressure in the suction duct 3, causes the fuel vaporization to be very effective mainly at low rpm of the engme.

Another pneumo-hydraulic calculating unit 32 according to the invention is shown in FIG. 2, wherein the fuel outlet chamber 31, the fuel reaction chamber 37 and the two chambers 49 and 51 fed with the air pressure are formedby bellows. Said bellows, however, instead of being aligned on the same axis and therefore acted on by opposed forces or thrusts asin the preceding embodiment, are on the contrary positioned in line and adjacent, and are subjected to forces which are all directed in the same direction, the equilibrium being obtained by means of a lever 61, which is fulcrumed at midway of its length by means of a cross support consisting of flexible blades 62, acting as a balance. The two bellows relating to the fuel (31 and 37) and the two bellows relating to the air (49 and 51) are fixed by their lower part to the body of the calculating unit and by their upper part to the said lever 61 symmetrically with respect to the fulcrum 62, whilst the shutter 53 is thrusted towards said lever 61 by a spring 66 tending to maintain in a closed condition the passage between the feeding chamber 54 and the outlet chamber 31.

The operation of this embodiment of the calculating unit is like that of the preceding one, except that, being now omitted any moving element, the pneumohydraulic calculating unit is capable of operating also in the overturned condition and therefore is particularly adapted for the use in aviation engines.

In FIG. 3 a modification according to the present invention of the pneumo-hydraulic calculating unit 32 of FIG. 2 is shown. In this case, the four chambers for the comparison of the air and fuel pressures are formed by suitably shaped cavities, provided in the body of the calculating unit and closed by a membrane 63 rigidly fixed to the balance 4 lever 61 by means of spacer blocks 64. According to FIG. 3 said balance lever 61 is fulcrumed at midway of its length by means of a flexible blade 65.

In the FIGS. 4 to 7 there are illustrated some ways for the correction of the mixture strength in order to temporarily enrich it on cold starting of the engine, as well as the related devices for obtaining such a manual or automatic enrichment of the mixture, according to the present invention. More particularly, in FIG. 4, said correction is carried out by acting on the pneumohydraulic calculating unit. To this end a spring 66 is as to act until a certain level of temperature exceeded.

The operation is simple. Until the engine is not running at normal temperature and thus the temperature of the engine head is lower than that of actuation of the thermostat, the latter continues to act through the solenoid on the pin 71, thus causing the same effect of the spring 66 to occur.

In the FIG. 5 the correction is effected by acting on the thermo-barometric compensation group by connecting the casing 24 to a pneumatic thermo-deviator 72, instead than to the stagnation zone 27 of the carburettor l. Said thermo-deviator consists of a box fixed to the engine head and connected, through the ducts 73 and 74, respectively to the said stagnation zone 27 and to a high pressure tank 75, the high pressure being generated by a compressor or'taken from the exhaust ducts of the engine. Within the said box a bimetallic plate 76 operates depending only on the temperature, for closing either one or the other of the ducts 73 and 74. The operation is as follows. Until the engine and therefore the head is warm (on starting) the bimetallic plate closes the duct 73 and transmits to the tank 24 the greater pressure of the tank 75 so that a temporary greater density of the air is simulated thus involving an enrichment of the mixture. When the engine is heated, its temperature causes the bimetallice plate 76 to snap, thus closing the duct 74, and the tank 24 is again in communication with the stagnation zone 27 of the carburettor.

According to FIG. 6 the correction is carried out by acting on the variable restriction device 16, more particularly by passing the orifice 18 through a hydraulic thermal switch 77 provided with a bimetallic plate 78.

Said thermal switch 77 is fixed to the cylinder head and connected by means of the ducts 79 and 80 respectively to the inlet 29 and to another inlet 81, downstream of the orifice 18, of the said variable restriction device 16 so that the bimetallic plate 78 leaves the conduit 80 open until the cylinder head of the engine is cold and closes it when the temperature increases. The cock 82 in the conduit 80 serves only to preset the extent of the by-pass during the calibration stage and can in reality be a simple calibrated orifice.

Finally, FIG. 7 illustrates a correction made by creating a dephasing in the coupling between the lever mechanism 14 and the pin 19 of the variable restriction device 16 by means of a soft iron wedge 83 placed between the registration screw 21 and the said pin 19, the said wedge being moved by the solenoid 84 of a thermostat 85 analogous to the already mentioned thermostat 69 and, like this last-named, fixed onto the cylinder head of the engine.

I claim:

1. A carburetor system for the continuous and precise control of the mixture strength in an injection carburation system for an Otto engine comprising: a carbuetor body having an air inlet, an internal stagnation area downstream of the air inlet, a throttle valve downstream of the stagnation area and a fuel injector downstream of the throttle valve; a pneumatic-hydraulic calculating unit having first and second counterposed chambers of equal effective areas acting on a moving element which moves in response to pressure differentials between the two chambers, said calculating unit having an outlet chamber and a reaction chamber of equal effective areas acting on opposite sides of the moving element and a feed chamber in communication with the outlet chamber; means for measuring fuel flow rate, said means including a variable restriction device which measures the fuel pressure drop between the upstream and downstream sides of an orifice which is choked by a pin; pressure-drop measuring meansfor measuring the flow rate the air upstream of said throttle valve, said means including a thin diaphragm inside the carburetor body choked by a shutter; lever means interconnecting said shutter and the pin of the variable restriction device and said throttle valve so as to ensure an equal degree of choking of said orifice and of said diaphragm for each angle of opening of the throttle valve; conduit means placing the upstream and downstream sides of said diaphragm in communication with said first and second counterposed chambers, respectively; conduit means placing the upstream side of said orifice in communication with said outlet chamber; fuel supply means for supplying fuel at constant pressure to said feed chamber, said means including a pump; conduit means for passing fuel from a location downstream of said orifice to said injector and to said reaction chamber of said calculating unit; a temperature and pressure compensating device for compensating for variations in air density, said device being in communication with the stagnation zone of the carbuetor body and connected to said variable restriction device so as to vary the choking of said orifice as a function of the temperature and pressure in said stagnation zone. 

1. A carburetor system for the continuous and precise control of the mixture strength in an injection carburation system for an Otto engine comprising: a carbuetor body having an air inlet, an internal stagnation area downstrEam of the air inlet, a throttle valve downstream of the stagnation area and a fuel injector downstream of the throttle valve; a pneumatic-hydraulic calculating unit having first and second counterposed chambers of equal effective areas acting on a moving element which moves in response to pressure differentials between the two chambers, said calculating unit having an outlet chamber and a reaction chamber of equal effective areas acting on opposite sides of the moving element and a feed chamber in communication with the outlet chamber; means for measuring fuel flow rate, said means including a variable restriction device which measures the fuel pressure drop between the upstream and downstream sides of an orifice which is choked by a pin; pressure-drop measuring means for measuring the flow rate of the air upstream of said throttle valve, said means including a thin diaphragm inside the carburetor body choked by a shutter; lever means interconnecting said shutter and the pin of the variable restriction device and said throttle valve so as to ensure an equal degree of choking of said orifice and of said diaphragm for each angle of opening of the throttle valve; conduit means placing the upstream and downstream sides of said diaphragm in communication with said first and second counterposed chambers, respectively; conduit means placing the upstream side of said orifice in communication with said outlet chamber; fuel supply means for supplying fuel at constant pressure to said feed chamber, said means including a pump; conduit means for passing fuel from a location downstream of said orifice to said injector and to said reaction chamber of said calculating unit; a temperature and pressure compensating device for compensating for variations in air density, said device being in communication with the stagnation zone of the carbuetor body and connected to said variable restriction device so as to vary the choking of said orifice as a function of the temperature and pressure in said stagnation zone. 